Abstract With the increasing utilisation of scrap in metallurgical processes due to recycling to reduce CO 2 footprint, the content of tramp elements in the base material is increasing. In order to quickly investigate the influence of tramp elements on the weld nugget microstructure and mechanical properties during resistance spot welding (RSW), a method has been developed to introduce tramp elements into the weld nugget. By making an indentation in one of the two sheets to be welded and inserting the desired quantity of tramp element before welding, the weld nugget can specifically be alloyed. This allows to quickly analyse the influence of individual tramp elements on the microstructure and its influence on the resulting mechanical properties. The applicability of the method was investigated using Cu as tramp element material. As part of the investigations, a targeted Cu content of 0.4 wt% was set, which was confirmed using energy-dispersive X-ray spectroscopy (EDS). The spot welds alloyed according to the method were compared with spot welds without the Cu addition and spot welds of an already Cu-alloyed material. The weld nugget microstructure of all steels analysed by light optical microscopy (LOM) and scanning electron microscopy (SEM) was martensitic with similar grain size and morphology, regardless of the Cu content. In tensile shear (TS) and cross tension (CT), testing plug failure occurred in all samples. The results from the TS tests with peak forces of 11.4–12.2 kN and absorption energies between 14.3 and 18.5 J were very close to each other. The CT results with peak forces of 6.7–8.5 kN and energies between 46 and 69 J showed a similar picture. The average weld nugget hardness of all three weld configurations was in between 383 and 398 HV1. The microstructural and mechanical results showed no significant differences. The presented method for a targeted weld nugget alloying during resistance spot welding allows a repeatable, easy and quick investigation of the influence of alloy modification by tramp elements such as Cu on the weld nugget properties and offers a practical approach to assess material changes due to an increased tramp element content.

Abstract For reasons of sustainability and cost efficiency, there is an increasing trend in the steel-processing industry to retrofit existing structures, avoiding costly shutdowns or dismantling. Although welding is a cost-effective joining method, it is rarely applied to old steels, whereas riveted or bolted connections are often uneconomical. Repair and refurbishment frequently require the replacement of damaged material or the creation of dissimilar old–new steel joints. Due to the varied manufacturing processes of historical steels, not all twentieth-century steels are inherently weldable, making an initial assessment of weldability essential. In this study, a historical non-deoxidized mild steel (produced by Siemens–Martin processing) originating from the construction of the Berlin Radio Tower (erected in 1926) was investigated using dilatometry to analyze its welding behavior. A database of welding CCT diagrams and HAZ simulations was established to support practice-oriented welding experiments, providing key insights into their weld-metallurgical behavior and weldability. Furthermore, initial welding trials were conducted, and the local residual stress states in dissimilar old–new steel joints were determined. These foundational investigations are critical for the development of innovative, load-adapted welding concepts for the repair and refurbishment of existing old-steel infrastructure in Germany.

Abstract This study proposes a comprehensive methodology for validating process parameters in pulsed gas metal arc welding (GMAW-P) applied to arc-based directed energy deposition, aiming at the production of weld beads with controlled geometry and process stability. Shadowgraphy was employed for metal transfer visualization, combined with stability analysis algorithms and metal transfer criteria. Fast Fourier transform (FFT) was applied to current and voltage signals to identify the most efficient pulse characteristics, droplet detachment behavior, and transfer frequency. An analytical formulation correlating wire feed rate, travel speed, and bead cross-sectional area was used to guide the selection of deposition parameters. In addition, a theoretical analysis of bead overlap was developed and its predictions were directly compared with experimental results, demonstrating good agreement and validating the proposed model. These strategies defined a stable working window with voltage between 22 and 28 V and current between 190 and 220 A. The optimal condition was obtained at a frequency of 240 Hz. The proposed methodology enables parameter adaptation for different materials, ensuring energy efficiency, cost reduction, and geometric consistency. Moreover, GMAW-P allows the production of high-quality deposits at lower current levels compared to conventional GMAW.

Abstract Additive manufacturing (AM) represents a category of manufacturing processes that fabricates parts in a layer-by-layer manner. As such, AM provides unique advantages over conventional manufacturing processes such as the ability to fabricate highly complex geometries, to minimize material waste, and to enable mass customization, while having some limitations, such as high costs and complexities. Advances in artificial intelligence (AI) and machine learning (ML) enable these limitations to be addressed due to the data-rich environment in modern commercial AM machines with multiple sensors. This paper surveys papers that apply AI/ML techniques to the topics of defect detection, AM process surrogate models and their application, generative design, and design for manufacturing in metal AM processes. The approach taken is to introduce these topics, provide a coarse survey, and then discuss specific applications in some depth, rather than to provide a fine-grained, comprehensive survey.

Abstract The energy transition and the goal of making Germany climate-neutral by 2045 have increased the demand for hydrogen as an energy carrier. Within this framework, the transportation and storage of hydrogen in liquid form at extreme low temperatures (> -196 °C) within welded steel containers need to be realized. In Europe, steels with a high nickel content like X8Ni9 are frequently used, but these steels are difficult to weld due to the magnetic remanence and have to undergo expensive post-weld heat treatments. In other regions of the world, the usage of medium manganese steels is more common. In this work, the focus is on the use of medium-manganese austenitic steels, which represent a more cost-effective, easier weldable, and readily available alternative to high-nickel steels. But in prior studies, it was shown that the strength of the weld metal using commonly available high-alloyed filler materials is not sufficient to meet the strength of the base material. To achieve this, this paper focuses on a slight alloy modification of the filler material to increase the strength of the weld metal. The toughness already matches the requirements of the industry. Overall, it is necessary to increase the strength of the material while ensuring adequate toughness. To modify the chemical composition of the weld metal, welding experiments with coating welding wires (using physical vapor deposition (PVD)) have been carried out. These coatings on the filler material can improve the mechanical properties, like strength and ductility of the weld metal. Furthermore, they can reduce the risk of cracking and other welding defects. For this study, the modification of the filler material was done by adding some amounts (< 1%) of Ni, TiN, Nb, and Ti. The medium-manganese austenite X2CrMnNiN17-7–5 (1.4371) is used as the base material. The steel under consideration is distinguished by elevated concentrations of manganese and nickel. These elements confer upon the steel distinctive mechanical properties, including elevated toughness at low temperatures and excellent weldability. A specific filler material, G 20 16 3 Mn N L, is used in the form of a wire with a diameter of 1.2 mm. The mechanical properties of the welded joint should correspond to those of the base material. It will be shown that due to the modification of the alloy composition of the filler material, the toughness and hardness of the weld metal can be influenced. It will be shown that the hardness, as an indicator of strength, can be increased by approximately 20HV compared to the weld metal of the unmodified filler wire. Especially, the addition of TiN could increase the hardness of the weld metal while keeping the toughness of the weld metal. Overall, the study will demonstrate that modifying the chemical composition of the filler material can be used to enhance the mechanical properties of the weld metal, thereby approaching the level of the base materials.